The invention is relative to a device for coating a flat substrate, with a coating module comprising a capillary slot which capillary slot is filled with a liquid coating medium and comprises an opening past which a surface of the substrate to be coated is to be conducted at a relatively small interval so that a coating layer is separated on said surface.
The invention is also relative to a method for coating a substrate, with a coating module past which the substrate with the surface to be coated is conducted, during which a coat of the coating medium is separated onto this surface, during which coating, a coating medium is supplied to the coating module.
A device of the cited species is known in the state of the art from U.S. Pat. No. 5,650,196 and WO 94/25177. For example, rectangular or round plates can be provided with a uniform coat of lacquer or varnish or other media which are liquid at first such as color filters or special protective coats with this device. This device is used especially in the field of thin-layer technology in the production of LCD screen monitors, masks for semiconductor manufacture and semiconductor or ceramic substrates. This device is distinguished in particular by a high uniformity of the laquer layer density, especially on rectangular plates, while using a small amount of laquer at the same time. For coating, the substrate with the surface to be coated is conducted downward over the capillary slot, which is designed so that as a result of the capillarity of the slot the coating medium is supplied automatically and at an especially uniform rate. Such a capillary action is achieved, e.g., with a slot less than 0.5 mm wide. As a result of the capillary action the coating medium rises automatically upward against the force of gravity in the slot and exits at the opening of the capillary slot. The intermolecular binding forces, the surface tension and the particularities of the surface perfusing (wetting) are decisive for this method. Customary coating rates are approximately 5 to 15 mm/s. Since the volumetric flow is essentially determined by the intermolecular binding forces the coating rate can not be significantly raised.
The invention is based on the problem of creating a device of the cited species which makes possible a significantly higher coating rate but nevertheless assures a uniform coat thickness with a low consumption of material.
The invention is solved in a generic device in that the capillary slot is open at the bottom and is filled via a supply chamber with coating medium and that the substrate is conducted below the opening of the slot with the surface to be coated facing up. In the case of the device in accordance with the invention the volumetric flow through the capillary slot is not only determined by the intermolecular binding forces but can be actively fixed. As a result, significantly higher coating rates, e.g., between 30 and 100 mm/s, can be achieved. The higher coating rate accordingly makes possible a greater production and therewith a significant lowering of the manufacturing costs.
An especially reliable filing of the coating chamber results if, according to a further development of the invention, an overflow container is provided which communicates via a liquid line with the capillary slot and is arranged above the opening of the capillary slot. The overflow container is preferably mounted so that it can be adjusted in its height. The height of the overflow container is proportional to the flowthrough of medium through the capillary slot and therewith to the coat thickness.
If the coating module comprises, in accordance with a further development of the invention, two plates arranged parallel to one another and a foil arranged between the latter, different capillary slots can be produced in a simple manner. This makes it possible to apply coating media with different viscosities and also to produce different coat thicknesses via the variable feed rate of the substrate below the capillary. Said capillary slot can be determined in a simple manner by a cutout or notch of the foil. The two plates can be detachably screwed to one another, for example. In this instance a replacing of the foil in order to change the width of the capillary slot is especially simple.
In the method of the invention, a volumetric flow takes place from above downward through the capillary slot during the coating and the substrate with the surface to be coated facing up is moved past the capillary slot.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.